Vibration characteristics and structural damping of rotating compressor blades

Nowadays, the increasing demand on the high efficiency energy, low fuel consumption and environment friendly leads the turbomachinery to be operating under a critical high rotation speed at high temperature and pressure. This severe operation condition will definitely increase the probability of the occurrence of the high cycle fatigue. To reduce the risk of appearing high cycle fatigue, the structural damping of turbomachinery components has to be increased. Since the structural damping is always positive while the aerodynamic damping can be negative at some situation, increasing structural damping is nevertheless an interesting field in turbomachinery research. One efficient way of increasing damping is to treat damping material over the blade surface. Traditional damping materials, such as rubber, are not applicable in the severe operation environment. Therefore, hard coating material is applied due to its high stiffness and good sustainability in rough environments. Numerical tools are developed to predict the structural damping of a dynamic rotating blade while varying several important designing parameters. Two types of rotating blades are modeled using the Hamilton’s principle: the straight blade by plate theory and pretwisted blade by shell theory. The extended Galerkin method and Chebyshev collocation method are applied for the numerical simulation, such as modal analysis and frequency response analysis. The parametric analysis is performed with respect to rotation speed, stagger angle, pretwisted angle, aspect ratio, etc. Proportional damping is used in all dynamic models to investigate the damping characteristics of the blades. Alternatively, a multilayer rotating blade is modeled by a high order layerwise theory, where the validated results reveal the modal damping exchanges between modes due to frequency loci veering and the influence of the damping configurations on the total damping of the multilayered structure. Finally, a commercial finite element software is used to predict the damping of a real compressor blade treated by the hard coating while varying the coating thickness and distributions